This invention relates to a bearing device in which a rolling bearing is fitted around an outer periphery of a shaft body such as a hub unit for vehicles and a method of manufacturing the same.
Such a vehicle-use hub unit as a bearing device generally has a structure wherein a double row rolling bearing is fitted around an outer periphery of a shaft body of a hub wheel so as not to come off.
The shaft body of the hub wheel is provided in a free end side thereof with a cylindrical portion used for the bearing not to come off. The cylindrical portion, formed by a turning work, is bent and deformed radially outward by a caulking jig, thereby being caulked on an outer end surface of an inner ring which the bearing equips to constitute a caulked portion. The bearing is prevented from coming off the hub wheel by the caulked portion, and simultaneously, the inner ring of the bearing is preloaded from the caulked portion.
When the cylindrical portion is caulked on the outer end surface of the inner ring of the bearing by abutting the caulking jig on an inner peripheral surface of the cylindrical portion, an abrasion occurs. As a result of the abrasion on the inner peripheral surface of the cylindrical portion caused by a friction thereof with the caulking jig, an abrasion powder is generated. An invasion of such abrasion powder inside of the bearing may shorten a life thereof.
Under the circumstances described above, a lubricant oil used to restrain the friction adheres to the abrasion powder, which makes it extremely difficult to remove the abrasion powder which has once invaded inside of the bearing.
Therefore, a main object of the present invention is to provide a bearing device capable of restraining such abrasion powder generated at a time of a caulking work with respect to a cylindrical portion and a method of manufacturing the bearing device.
Other objects, features and advantages of the present invention will be apparent from the described hereafter.
A bearing device of the present invention comprises a shaft body having, in a free end side thereof, an axial caulking cylindrical portion and a rolling bearing fitted around an outer periphery of the shaft body. The cylindrical portion is bent radially outward to be caulked on an outer end face of an inner ring of the rolling bearing. A surface roughness of the inner peripheral surface of the cylindrical portion is set to a value equivalent to or less than a roughness corresponding to a life ratio regulated with respect to a bearing device having a standard life.
A shape of the cylindrical portion comprises all kinds of shapes such as a radial wall thickness is uniform, becomes gradually thinner or varies stepwise intermediately toward the free end side of the shaft body.
The machine work comprises a turning work using a turning tool, a drilling work using a drill and other works using other machine tools.
According to the bearing device of the present invention, the surface roughness of the inner peripheral surface of the cylindrical portion is set to a value corresponding to a life ratio regulated with respect to a bearing device having a standard life. Therefore, when the caulking jig is abutted on the inner peripheral surface of the cylindrical portion in order to caulk the cylindrical portion on the outer end surface of the inner ring of the bearing, an amount of abrasion powder generated therein is restrained despite a strong contact of the caulking jig with the inner peripheral surface of the cylindrical portion. Consequently, a life of the bearing is favorably lengthened by a decreased amount of the abrasion powder which invades inside of the bearing.
Also, such a laborious work as eliminating the oil-adhered abrasion powder from inside of the bearing becomes unnecessary.
As a preferable embodiment of the present invention, the surface roughness of the inner peripheral surface of the cylindrical portion is set to a value of 14.0 xcexcm or less in a ten-point mean roughness (Rz).
As a preferable embodiment of the present invention, the surface roughness of the inner peripheral surface of the cylindrical portion is set to a value of 12.5 xcexcm or less in a ten-point mean roughness (Rz).